Probem with Ports/boundaries in CST MWS

Hello,

i am trying to simulate a suspended stripline filter actually, but as i am new to CST i have some basic problems.

I tried to simulate Microstrip line (Ro4350 lossy 50 Ohm line made of Gold). I dont have bottomside metallization, as i am using electric walls on all sides. Now i first only set one port at the beginning of the line (substrate edge), the waveguide end was obviously shorted by the electric boundary when i examined the smith chart. Phase-shift was believable also.

When i set a second port at the other end of the line, i have non-believable results. S11 is lower than -60 dB and S21 neglectably low and Smith Chart is only one single matched dot. When i considerably change MS line width, results basically stay the same, although port impedance changes correctly...

I really don't know whats happening there i just do not get resonably results with 2 ports. Btw i am using the planar filter preset.

Can anyone help please?!

Chris

what material do you have below the microstrip line? A mistaken setting there could explain your results.

I have used lossy and loss-free RO4350 material in the correct thickness for this line. Metallization thickness is 35um.

without more details it is hard to say anything. But no transmission and no reflection suggests wrong parameters somewhere.

If you use electric walls, you should increase the distance to the side walls and to the top cover.

From what I remember, depending on the simulator settings, you will get S-parameters that are normalized to a fixed impedance (such as 50 Ohm) or S-parameters relative to the line impedance at the ports. I assume you have the second case. Check if there is some option to normalize the results to 50 Ohms.

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